\documentclass{standalone}
\usepackage{mathtools}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
\draw [thin,->] (-3,0)--(3,0) node[below]{$x$};
\draw [thin,->] (0,-1.1)--(0,4) node[left]{$\operatorname{erf}'(x)$};






\draw[red] plot[domain=-3:3,smooth] function {2/sqrt(pi)*exp (-x**2)};

\draw[green] plot[domain=-3:3,smooth] function {1/sqrt(pi)*exp (-x**2/4)};

\draw[magenta] plot[domain=-3:3,smooth ] function {4/sqrt(pi)*exp (-4*x**2)};
\draw[blue] plot[domain=-3:3,smooth ] function {6/sqrt(pi)*exp (-9*x**2)};





\end{tikzpicture}
\end{document}



